We evaluate the efficacy of repellents against chigger mites on humans according to guideline OPPTS 810.3700 of the Environmental Protection Agency of the US. Figure 1 shows a modified test procedure, wherein a mite is placed on a metal plate affixed to the skin of a test subject. We observe whether or not the mite walks off the metal plate and a certain distance onto the skin. Chigger mite tests can only be performed in September/October, when chigger mites are available in the field.
Fig. 1: Larva of chigger mite (left center) at the edge of the metal plate, being repelled by a repellent on the skin.